1. Field of Invention
The present invention relates to a fret saw including a cutting wire provided, by electroplating, with fixed abrasive grains each including a core coated with a hard film and, more particularly, to a fret saw including a cutting wire provided with fixed abrasive grains each including a metal or alloy core coated with a diamond or boron nitride film.
2. Related Prior Art
Electro-optical industry has been booming recently, and there are growing needs for silicon wafers, sapphire and agate that are hard. The silicon wafers are needed for the development of integrated circuits (“IC”). In the production of the IC, a wafer-slicing process is needed. The wafer-slicing process however often causes loss of materials, and the cost of the wafer-slicing process is therefore high. Obviously, there is a need for an excellent wafer-slicing process.
The wafer slicing may be conducted by a fret saw together with abrasive materials. The abrasive materials are classified into free abrasive grains and fixed abrasive grains. The free abrasive grains are included in abrasive paste and the abrasive paste is provided onto the fret saw in the wafer slicing. The wafer slicing by the free abrasive grains and the fret saw is not efficient, not precise and not environmentally friendly. The fixed abrasive grains are provided on the surface of the fret saw by adhesion, electroplating or electroless plating. The wafer slicing by the fixed abrasive grains and the fret saw is relatively efficient, precise and environmentally friendly. Therefore, the fret saws are used with the fixed abrasive grains in most cases to promote the efficiencies.
Fixed abrasive grains are generally super hard abrasive grains made of cubic boron nitride (“CBN”) or diamond. The super hard abrasive grains are bonded to a cutting wire by synthetic resin or electroplating. The super hard abrasive grains could be detached from the cutting wire more easily where the super hard abrasive grains are bonded to the cutting wire by the synthetic resin than where the super hard abrasive grains are bonded to the cutting wire by the synthetic resin. It however takes longer to bond the super hard abrasive grains to the cutting wire by electroplating than by synthetic resin. To increase the speed of the production of the fret saws, there have been various attempts to coat Ti, Ni or Cu on the super hard abrasive grains. However, the super hard abrasive grains pile up during the electroplating and some of them are detached from the cutting wire inevitably. This is a waste of the super hard abrasive grains and reduces the life of the fret saws.
To overcome the foregoing problem, as disclosed in U.S. Pat. No. 7,704,127, “Electrodeposited Wire Tool”, the thickness of the metal coating on a super hard abrasive grain is controlled to be smaller than 0.1 micrometer and is preferably 0.05 micrometer. Alternatively, the weight of the metal coating is controlled to be smaller than 10% and preferably 5% of the weight of a super hard abrasive grain. Thus, the super hard abrasive grains are not made with excessively high electric conductivity. Hence, the super hard abrasive grains do not pile up during the electroplating. Moreover, the speed of the electroplating exceeds 1 meter/minute. The super hard abrasive grains are made of diamond that is expensive. The super hard abrasive grains are often very different from one another in size and shape. Therefore, when the fret saw is used to slice a wafer or sapphire, the Kerf loss is high, and V-shaped notches could easily occur.
There have been attempts to merge diamond with metal to form super hard abrasive grains. However, it is still difficult to control the shapes of the super hard abrasive grains. The costs of the super hard abrasive grains are still high. The super hard abrasive grains still pile up during the electroplating.
Diamond films have gained a lot of attention since 1980s. There were many researches for diamond films around the world from mid 1980s to late 1990s. Diamond films are often used in optical components, microelectronic components, surface acoustic wave (“SAW”) devices and radiation-resistant electronic components. Most of the efforts were made on the diamond films and equipment for making the diamond films. Only a few of them were made on the use of the diamond films on tools such as polishing tools, milling cutters, welding tools, wire-drawing die cores, grinding wheels and precision bearings for example. For instance, CemeCon has built a CCDia production line.
However, the super hard abrasive grains made of diamond are expensive. Moreover, the super hard abrasive grains made of diamond must be coated with metal to increase the speed of the electroplating. Furthermore, it is difficult to control the shapes and sizes of the super hard abrasive grains made of diamond, and it is a waste of time and cost to screen the super hard abrasive grains made of diamond.
The present invention is therefore intended to obviate or at least alleviate the problems encountered in prior art.